Syntheses, Structures, and Mössbauer Effect Spectroscopy of Triple-Decker Complexes Incorporating Nonamethylferrocene

Three
new triple-decker complexes were synthesized by the reaction
of nonamethylferrocene, Cp′FeCp* (Cp′ = C5Me4H, Cp* = C5Me5), with coordinatively
unsaturated transition-metal complexes. The reaction of ruthenium
cations [(C5R5)­Ru]+ (R = H, Me) with
Cp′FeCp* afforded the purple heterometallic triple-decker complexes
[(C5R5)­Ru­(μ-Cp′)­FeCp*]+ by electrophilic addition of ruthenium to the Cp′ ring of
nonamethylferrocene. The analogous reaction with the manganese cation
[Mn­(CO)3]+ produced the blue homometallic triple-decker
complex [Cp*Fe­(μ-Cp′)­FeCp*]+ by abstraction
of the Cp′ ring from Cp′FeCp* and subsequent addition
of the newly generated cation [Cp*Fe]+ to 1 equiv of Cp′FeCp*.
These experiments demonstrate that the asymmetry of Cp′FeCp*
gives rise to a remarkable degree of regioselectivity such that ruthenium
electrophiles add only to the Cp′ ring and never to the Cp*
ring. In a similar way, [Mn­(CO)3]+ abstracts
only the Cp′ ring from Cp′FeCp* to produce [Cp*Fe]+, which in turn adds only to the Cp′ ring of Cp′FeCp*
to produce [Cp*Fe­(μ-Cp′)­FeCp*]+. Three air-stable
triple-decker complexes incorporating nonamethylferrocene, [Cp*Fe­(μ-Cp′)­FeCp*]+ (1), [CpRu­(μ-Cp′)­FeCp*]+ (2), and [Cp*Ru­(μ-Cp′)­FeCp*]+ (3), have been characterized by NMR spectroscopy, elemental
analysis, single-crystal X-ray diffraction analysis, and temperature-dependent 57Fe Mössbauer spectroscopy.